CN111622828A

CN111622828A - Ammonia gas generation metering injection device

Info

Publication number: CN111622828A
Application number: CN202010453019.7A
Authority: CN
Inventors: 齐宝华
Original assignee: Ningbo Kaishi Environmental Protection Technology Co ltd
Current assignee: Ningbo Kaishi Environmental Protection Technology Co ltd
Priority date: 2020-05-26
Filing date: 2020-05-26
Publication date: 2020-09-04

Abstract

The invention discloses an ammonia gas generation metering injection device, which comprises a metering injection control unit, a hollow container with an ammonia generation chamber, a cover, a solid reducing agent, an electric heater, a liquid discharge pipeline with a liquid discharge valve positioned at the bottom of the hollow container, gas release pipes which are positioned on the solid reducing agent and used for releasing gas accumulated in the solid reducing agent and are uniformly provided with openings, an exhaust passage communicated with the ammonia generation chamber through a check valve, an electric control valve and an exhaust pipeline in sequence, and an electric heating line positioned in the exhaust pipeline, wherein the gas release pipes are provided with openings; the ammonia generating chamber is internally provided with a first pressure sensor, a first temperature sensor and a second temperature sensor, and the metering injection control unit is respectively connected with the electric heater, the electric heating wire, the electric control valve, the first pressure sensor, the first temperature sensor and the second temperature sensor through signal wires; the driving signal of the electric heater is a voltage pulse signal having a high current signal and a low current signal. The present invention can precisely control the release rate of ammonia.

Description

Ammonia gas generation metering injection device

Technical Field

The invention relates to an ammonia gas generating and conveying device, in particular to an ammonia gas generating, metering and injecting device.

Background

Selective Catalytic Reduction (SCR) technology has been widely used to reduce NOx emissions from internal combustion engines, particularly diesel engines. In an SCR system, it is generally necessary to mix ammonia (NH3) with the exhaust gases of the engine and then pass through a catalyst where the ammonia reacts with NOx in the exhaust gases and reduces the NOx to nitrogen and water. Due to safety considerations and transport and storage difficulties, in SCR systems ammonia is usually produced from a precursor (e.g. urea) rather than being used directly. The precursor is also referred to herein as a reducing agent.

Both solid and liquid reductants can be used in the SCR system. The solid reducing agent may be directly decomposed to generate ammonia, for example, metal amine salts including magnesium ammonium chloride (Mg (NH3)6Cl2), calcium ammonium chloride (Ca (NH3)8Cl2), and the like, and ammonium salts including ammonium carbamate (NH 4COONH 2), ammonium bicarbonate (NH 4HCO3), ammonium carbonate ((NH4)2CO3), and the like may be decomposed at a relatively low temperature to generate ammonia. Solid reducing agents have many advantages over liquid urea solutions (such as 32.5% strength automotive urea solution or DEF), including no freezing temperatures, no deposits in the decomposition tubes, higher density and lower volume, insensitivity to impurities in the reducing agent, and no additional energy required to heat the water in the urea solution. However, one significant obstacle to the use of solid reductants is the metering injection of the reductant, including high energy consumption, pressure variation, and injection rate control issues. These problems make it difficult to accurately meter the amount of ammonia injection in an SCR system.

Generally, ammonia is produced using a solid reducing agent, and as described in Chemical Engineering Science 61(2006) 2618-2625, the reducing agent in a closed vessel is heated and then ammonia gas is injected into the off-gas after a certain pressure is reached. Since all the reducing agent in the container is heated when heating the solid reducing agent, a relatively high heating power is required, and also, when the amount of reducing agent is large, control of the pressure in the container is difficult due to a time delay caused by heat transfer. The instability of the pressure affects the ammonia injection accuracy, especially in the absence of feedback control. This may add significant complexity and cost to the system. In addition, too high a pressure may also cause safety hazards.

In addition to the metal amine salt, the ammonia carrier generates not pure ammonia gas but a mixed gas in which substances such as carbon dioxide and water are mixed when the ammonium salt is decomposed by heating. Therefore, when using these ammonium salts as reducing agents, inaccuracies in the dosing can also result from varying ammonia content in the effluent if only the mass flow rate of the effluent is controlled.

Thus, there is a need to solve the above problems.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide an ammonia gas generation metering injection device which can accurately control the release rate of ammonia.

The technical scheme is as follows: in order to achieve the above purpose, the invention discloses an ammonia gas generation metering injection device, which comprises a metering injection control unit, a hollow container with an ammonia generation chamber, a cover adapted to the hollow container, a solid reducing agent positioned in the ammonia generation chamber, an electric heater positioned in the ammonia generation chamber, a liquid discharge pipeline positioned at the bottom of the hollow container and provided with a liquid discharge valve, gas discharge pipes which are positioned on the solid reducing agent and used for discharging gas accumulated in the solid reducing agent and are uniformly provided with openings, an exhaust passage which is communicated with the ammonia generation chamber through a check valve, an electric control valve used for controlling the ammonia injection rate and an exhaust pipeline in sequence and used for discharging ammonia gas, and an electric heating wire positioned in the exhaust pipeline; the ammonia generating chamber is internally provided with a first pressure sensor for sensing the internal pressure, a first temperature sensor for sensing the internal gas temperature and a second temperature sensor for sensing the solid reducing agent temperature, and the metering injection control unit is respectively connected with the electric heater, the electric heating wire, the electric control valve, the first pressure sensor, the first temperature sensor and the second temperature sensor through signal wires; the driving signal of the electric heater is a voltage pulse signal having a high current signal and a low current signal.

The closed-loop temperature control module of the electric heater comprises a current detection module, a pulse controller, a pulse width modulation generator and a driver, wherein the current detection module detects the current of the electric heater and sends a detection signal to the pulse controller, the pulse controller generates a signal duty ratio according to the detection signal and the temperature duty ratio and sends the signal duty ratio to the pulse width modulation generator, the pulse width modulation generator generates a pulse width modulation signal with a fixed period according to the signal duty ratio and sends the pulse width modulation signal to the driver, the pulse width modulation signal is converted into a driving signal in the driver, and then the driving signal is sent to the electric heater through the current detection module.

Preferably, the pulse controller comprises a current measuring module, a temperature calculating module and a temperature pulse control module, the current measuring module converts the detection signal into a digital value, the temperature calculating module calculates the resistance value of the electric heater according to the digital value, then calculates the temperature value of the heater according to the temperature resistance curve of the electric heater, and the temperature pulse control module obtains the signal duty ratio according to the temperature value and the temperature duty ratio of the heater.

Further, the control method of the temperature pulse control module comprises the following steps:

(1) if the mark PulseFlag is 1, if so, turning to (2), otherwise, turning to (6);

(2) incrementing a counter TimerON, wherein the TimerON is TimerON + 1;

(3) comparing the value of TimerON with the value of Tp T _ Dc/T, where Tp is the period of the temperature control pulse, T _ Dc is the duty cycle of the temperature control pulse, and T is the period of the timer interrupt, and determining that TimerON ≧ Tp T _ Dc/T? If yes, turning to (4), otherwise, turning to (5);

(4) the counter TimerON is equal to 0, the flag PulseFlag is equal to 0, and the procedure is ended;

(5) starting a temperature PID controller, and ending the program;

(6) checking the value of a variable PulseFlag (K-1) of the previous period, judging whether the PulseFlag (K-1) is 1, if so, turning to (7), otherwise, turning to (8);

(7) closing the temperature PID controller and resetting, and setting the signal duty ratio PWM _ Dc to be zero;

(8) incrementing a counter timerfoff, which is timerfoff + 1;

(9) comparing the TimerOFF value with Tp (1-T _ Dc)/T, determining that TimerOFF is not less than Tp (1-T _ Dc)/T? If yes, turning to (10), otherwise, ending the program;

(10) the counter timerfoff is equal to 0, the flag PulseFlag is equal to 1, and the routine ends.

And the pressure control module is used for generating a temperature duty ratio signal, and the temperature duty ratio signal is calculated and generated according to an error value obtained by comparing a pressure sensing value obtained by the first pressure sensor with a target pressure value.

Preferably, the ammonia generator further comprises a heat exchanger located in the ammonia generating chamber and a coolant passage for flowing engine coolant and connected with the heat exchanger through a control valve, and the metering injection control unit is connected with the control valve through a signal line.

Further, the control method of the control valve includes the steps of: the pressure sensing value of the first pressure sensor is compared with a low pressure threshold value Thd _ PLo and a high pressure threshold value Thd _ Phi respectively, the control valve is electrically opened when the obtained pressure sensing value is smaller than the low pressure threshold value Thd _ PLo, and the control valve is electrically closed when the pressure sensing value is larger than the high pressure threshold value Thd _ Phi.

Has the advantages that: compared with the prior art, the invention has the following remarkable advantages:

(1) the solid reducing agent is placed in an ammonia generating chamber, a driving signal of an electric heater is a voltage pulse signal with a high current signal and a low current signal, each pulse comprises a high-temperature part and a low-temperature part, the surface temperature of the electric heater in the high-temperature part is higher than the ammonia release temperature, and the surface temperature of the electric heater in the low-temperature part is lower than the ammonia release temperature; using the pulse signal, the reducing agent adjacent to the electric heater releases ammonia only when the surface temperature is higher than the ammonia release temperature; thus, the release speed of ammonia can be controlled by controlling the duty ratio of the temperature pulse; the resistance of the electric heater when controlling the electric heater is used to generate a temperature pulse in a closed loop control, and the PWM generator drives the electric heater.

(2) The present invention further has a pressure sensor inside the ammonia generating chamber for sensing a pressure inside thereof, the pressure sensing value maintaining the pressure of the container within a predetermined range through the pressure control module, comparing a constant target pressure value with a sensing value obtained from the pressure sensor, and the pressure control module generating a temperature duty command using an error or difference between the two values for controlling the temperature pulse control module; with dual loop control, i.e., with pressure loop and temperature loop control, the pressure inside the ammonia generation chamber can be precisely controlled by the ammonia release rate.

Drawings

FIG. 1 is a schematic illustration of an engine system having an SCR exhaust treatment system according to the present disclosure;

FIG. 2 is a schematic structural diagram of an ammonia gas generation metering injection device in the invention;

FIG. 3 is a graph of the applied voltage of the electric heater, the temperature response and the ammonia release rate in the present invention;

FIG. 4 is a schematic diagram of a closed loop temperature control module according to the present invention;

FIG. 5 is a schematic diagram of a pulse controller according to the present invention;

FIG. 6 is a schematic flow chart of a temperature pulse control module in the pulse controller according to the present invention;

FIG. 7 is a schematic diagram of a pressure control module of the present invention;

FIG. 8 is a block diagram of an injection rate control system of the present invention;

FIG. 9 illustrates a control method for generating the first two PWM signals in the injection rate control system of the present invention;

fig. 10 is a control method for generating a third level PWM signal in the injection rate control system according to the present invention.

Detailed Description

The technical scheme of the invention is further explained by combining the attached drawings.

As shown in fig. 1, in the engine system, exhaust gas generated by engine 100 enters passage 120 through manifold 101. The passage 120 is fluidly connected to an ammonia gas generating metering jet device 200 which is controlled by an Engine Control Unit (ECU) 108 via signal line 107. The ammonia-generating metering jet device 200 delivers and mixes the reductant with the exhaust gas. The mixed exhaust gas flows through the passage 130 into the catalyst 103 where the reductant reacts with and reduces NOx in the exhaust gas. On the passage 120, a third temperature sensor 102 is used to measure the temperature of the exhaust gas upstream of the catalyst 103, and a temperature sensing signal is sent to the ECU108 via the signal line 106. The fourth temperature sensor 104 is mounted on a tailpipe 110 that is fluidly connected to the catalyst 103. A fourth temperature sensor 104 is used to measure the temperature of the exhaust gas downstream of the catalyst 103, and the signal obtained from this temperature sensor is transmitted to the ECU108 via a signal line 109. In addition, a NOx sensor 105 is provided on the tail pipe 110 for measuring the NOx emission level of the exhaust pipe, and a signal obtained from the NOx sensor 105 is sent to the ECU108 through a signal line 111.

One embodiment of an ammonia production metering jet device 200, shown in fig. 2, within which engine coolant first enters coolant passage 421 and enters heat exchanger 455 through control valve 420. The control valve is controlled by a metered injection control unit (DCU) 440 via signal line 413, and DCU440 communicates with ECU108 via signal line 107 (not shown in fig. 2 a). The heat exchanger 455 and an electric heater 407 are both located in the ammonia generating chamber 457 of the hollow vessel 430. The electric heater 407 is controlled by the DCU440 via signal line 412. Solid reductant 458 is also present in ammonia generating chamber 457, hollow container 430 fits into lid 425, and at the bottom of container 430 there is a purge valve 422 and a purge line 423, and excess liquid generated by the solid reductant can be purged through purge line 423 by opening purge valve 422. In the ammonia generating chamber 457, there is also a gas release pipe 459 in which openings 461 are uniformly distributed for releasing gas generated inside the solid reducing agent 458 accumulated. The ammonia generating chamber 457 is fluidly connected to the exhaust passage 432 through a check valve 406, an electrically controlled valve 405, and an exhaust line 446. The exhaust line 446 has an electrical heater line 445 therein, and the solenoid valve 405 and electrical heater line 445 are controlled by the DCU440 via

signal lines

416 and 417, respectively. Inside the ammonia generation chamber 457, there is a first pressure sensor 426 for sensing the pressure therein. The gas temperature inside the ammonia generating chamber 457 is measured by the first temperature sensor 410, and the first temperature sensor 410 and the first pressure sensor 426 are connected to the DCU440 through

signal lines

414 and 415. The temperature of the solid reductant in the ammonia generating chamber 457 is measured by the second temperature sensor 401 and sent to the DCU440 via signal line 411. The flow rate of ammonia gas under the internal pressure of the ammonia generating chamber 457 is controlled by the electronic control valve 405 by varying the opening time in a certain period. To reduce heat loss within the ammonia generation chamber 457, the ammonia generation chamber housing 448 may also be coated or contain a layer of insulation.

Unlike liquid reductant solutions, solid reductants are difficult to meter. Typically, when a solid reductant is used, it needs to be heated to the decomposition temperature to release ammonia. However, heating the solid reducing agent in bulk is time-consuming and energy-consuming, which is particularly problematic when electrical heating is used. In order to accelerate the decomposition of the solid reducing agent, in fig. 2a, the electric heater may use a special pulse control. The pulse in the pulse control consists of two signals of high current and low current, when the high current signal is applied to the electric heater, the heater can generate temporary high surface temperature, and the temperature can decompose the solid reducing agent near the heater. When the signal is changed into low current, the surface temperature of the heater is reduced, and meanwhile, the surface temperature of the heater is further reduced by the heat energy absorbed by the solid reducing agent in the decomposition process. The solid reductant decomposition process is stopped when the solid reductant temperature is below the decomposition temperature, and therefore the average ammonia release rate in this pulse control is determined by the duty cycle of the applied current pulses. Unlike the PWM control that is generally used in the heating control, in this particular pulse control, the temperature of the solid reducing agent is pulsed, rather than controlled to a steady value or interval; the stability of the temperature is not the target of this pulse control.

In fig. 2, a simple temperature control is to apply a voltage pulse to the electric heater 407, as shown in fig. 3, when the voltage pulse is applied, the heater surface temperature rises, and when the heater temperature is higher than the ammonia release temperature, the solid reducing agent decomposes and generates ammonia. The rate of ammonia production is determined by the heater temperature, and the higher the heater temperature, the higher the rate of ammonia production. When the voltage pulse is turned off, the surface temperature of the heater drops, and when the temperature of the heater drops below the decomposition temperature, the solid reducing agent stops decomposing.

The temperature pulse can be further controlled in a closed loop, while the heater surface temperature can also be detected by measuring the resistance of the heater when the temperature resistance characteristics of the electric heater are known. As shown in fig. 4, in a closed loop temperature control system, the current detection module 247 detects the current in the electric heater 206 and sends a detection signal to the pulse controller 250. This sensed signal and a temperature duty cycle command are used in the pulse controller 250 to generate a signal duty cycle command that is then sent to the pulse width modulation generator 249. A pulse width modulation signal (PWM) generated by the pulse width modulation generator 249 is converted into a driving signal in the driver 248 and then is applied to the electric heater 206 through the current detection module 247 and the signal line 242.

The current sensing in the current sensing module 247 can be implemented using a variety of methods. For example, one simple method is to measure the voltage drop across a shunt resistor connected in series to the electric heater 206. And in driver 248, a switching circuit may be used to generate the drive signal. In the pwm generator 249, a pwm signal having a fixed period may be generated by the control logic circuit in accordance with a duty command of a signal supplied from the pulse controller 250.

The pulse controller 250 may implement closed loop control, where the pulse controller 250 uses the sensed signal from the current detection module 247 as feedback, and then generates a signal duty cycle command based on the sensed signal and the temperature duty cycle command and provides it to the pulse width modulation generator 249. One implementation of pulse controller 250 is shown in fig. 5. In the pulse controller 250, the sensing signal obtained from the current detection module 247 is converted into a digital value in the current measurement module 281, and is used to calculate the resistance value of the electric heater 206 in the temperature calculation module 282, and then the heater temperature value is calculated according to the temperature resistance curve of the electric heater. The heater temperature value and the temperature duty cycle command are then compared in the temperature pulse control module 283 and a signal duty cycle command is generated and sent to the pulse width modulation generator 249.

The analog to digital conversion in the current measurement module 281 may be implemented by an analog to digital converter (ADC), while the resistance and temperature calculation in the temperature calculation module 282 may be implemented by a program running in a microprocessor in which the heater temperature may be calculated by a table look-up method using a table with heater resistance value inputs, and the table may be populated with the temperature resistance curve or data of the electric heater.

Various control methods can be used in the temperature pulse control module 283, such as a PID-based pulse control, which is one of the methods, and the method can be implemented by the interrupt service routine shown in fig. 6, which is triggered by a timer and can be run periodically. As shown in fig. 6, after the program starts to run, the flag PulseFlag is checked first. If the PulseFlag value is 1, the counter TimerON is incremented. The value of TimerON is then compared to the value of Tp T _ Dc/T, where Tp is the period of the temperature control pulse, T _ Dc is the duty cycle of the temperature control pulse, and T is the period of the timer interrupt. If the value of TimerON is less than Tp T _ Dc/T, then temperature PID control is enabled and the routine ends. Otherwise, the routine ends after the timer is reset to zero, and a value of zero is assigned to the flag variable PulseFlag. In the step of checking the value of PulseFlag, if it is not 1, the value of the variable PulseFlag (K-1) of the previous cycle is checked. If the value of PulseFlag (K-1) is 1, i.e., the PulseFlag value changes from 1 to zero, the PID controller is turned off and reset, and the signal duty command PWM _ Dc is set to zero. The value of the counter timerfoff is then incremented and the incremented value of timerfoff is compared to Tp (1-T _ Dc)/T. If the TIMEROFF value is less than Tp (1-T _ Dc)/T, the process ends, otherwise, the process ends after resetting the counter TimeOFF to zero and assigning a value of 1 to the flag PulseFlag.

In fig. 4, the temperature duty cycle command input to the pulse controller 250 may be generated by pressure control as shown in fig. 7. This pressure control is used to control the pressure in the ammonia generating chamber 457 to a target pressure value. In the pressure control of fig. 7, a target pressure value is first compared with a pressure sensing value obtained from the first pressure sensor 426 of the ammonia generating chamber 4577, and a comparison error is generated by the pressure control module 285 as a temperature duty command. The pressure control module 285 is a feedback controller and may use a variety of control methods including PID control and relay control.

In fig. 2, when the coolant temperature is higher than the decomposition temperature of the solid reducing agent in the ammonia generating chamber 457, the control valve 420 may be electrically opened to pass the coolant through the heat exchanger 455 to heat the solid reducing agent. When coolant heating is enabled, there are a variety of methods that may be used to control the control valve 420. One simple method is relay control, which compares the pressure sensing value with a low pressure threshold value Thd _ PLo and a high pressure threshold value Thd _ Phi. In this method, when the pressure sensing value obtained from the first pressure sensor 426 is smaller than the low pressure threshold value Thd _ PLo, the control valve 420 is electrically opened, and if the pressure sensing value is larger than the high pressure threshold value Thd _ PHi, the control valve 420 is electrically closed. When coolant heating is operating simultaneously with electrical heating, the thresholds Thd _ PLo and Thd _ PHi may be determined according to the requirements for system performance. For example, when precise pressure control is required, the high pressure threshold value Thd _ Phi may be set slightly lower than the target pressure value. In this manner, coolant heating is used as a coarse control, while precise pressure control is "fine tuned" by electrical heating. If it is desired to reduce the electrical heating consumption, the low pressure threshold value Thd _ PLo may be set higher than the target pressure value. In this manner, when the coolant is able to bring sufficient heat energy, the electric heater 455 is de-energized, thereby saving power.

The ammonia injection rate of the ammonia gas generating metering injector 200 shown in fig. 2 can be achieved in two steps. The first step is to calculate the ammonia content, C, in the ammonia generation chamber 457_{NH3_457}The second step is the command provided by the SCR control by means of pulse width modulation, R_NH3Ammonia content in the ammonia generating chamber 457, C_{NH3_457}And a pressure sensing value, P, obtained from first pressure sensor 426₄₂₆The ammonia injection rate is controlled by controlling the opening time, Dc3, of the electrically controlled valve 405 in repeated cycles such that the injection rate reaches R_NH3The value of (c). As mentioned above, there are two main classes of solid reducing agents, one is a metal amine salt, which produces pure ammonia when decomposed by heating, so that the ammonia content in the first step can be set to a constant value, such as C_{NH3_457}＝1.0。

Another class is ammonium salts, which produce other substances in addition to ammonia, such as water, carbon dioxide, etc., during decomposition. Therefore, when the ammonium salt is used, it is necessary to calculate the ammonia content from the state in the ammonia generating chamber 457. In the ammonia generation chamber 457, when the decomposition reaction of the ammonium salt reaches an equilibrium state, the ammonia content in the gas is determined by the gas pressure therein, the gas temperature, and the liquid temperature, as a function of these three parameters:

C_{NH3_457}＝f(P₄₂₆,T₄₁₀,T₄₀₁)

in which C is_{NH3_457}Is the ammonia content, P, in the ammonia generation chamber 457₄₂₆Is the gas pressure, T, measured by first pressure sensor 426₄₁₀Is the gas temperature measured by the first temperature sensor 410, and T₄₀₁It is the solid reductant temperature measured by the second temperature sensor 401. In actual control, the algorithm in FIG. 7 may control the pressure in the ammonia generation chamber 457 to a target pressure with ammonia content C_{NH3_457}The calculation of (a) can be performed by first calculating an initial value from the liquid temperature and the gas temperature, and then further compensating according to the gas pressure. The specific implementation can be accomplished by two table lookup operations:

C_{NH3_ini}＝Tbl1(T₄₁₀,T₄₀₁)

C_{NH3_457}＝Tbl2(P₄₂₆,C_{NH3_ini})

wherein the values in tables Tbl1 and Tbl2 may be determined experimentally.

In the second step of ammonia flow control, three-level PWM control may be used to generate a signal for controlling electronically controlled valve 405. As shown in FIG. 8, in this control, first, an ammonia injection rate command (R) is generated by the SCR control_NH3) And the calculated ammonia concentration (C)_{NH3_457}) A gas flow command is calculated by a flow command calculation module 290. The commanded gas flow is then calculated in a target value calculation block 286 along with the first stage PWM cycle set point to obtain a pulse width target value. Meanwhile, in a model block 287, a current pulse width signal may be calculated based on the pressure sensing signal. This current pulse width signal is compared to a pulse width target value and the resulting error is counted along with the second level PWM period set point via the second level PWM duty cycle calculation module 288The duty cycle value Dc2 of the second stage PWM signal is calculated. To achieve a fast response while avoiding overheating, it is generally desirable to provide pull-in and hold voltages when controlling the electrically controlled valve 405. This voltage control may be achieved by adjusting the duty cycle Dc3, and the duty cycle Dc3 may be generated in the third stage PWM signal duty cycle generation module 289 according to Dc 2.

As shown in fig. 8, the target value calculation module 286, model module 287, second stage PWM duty cycle calculation module 288 and flow command calculation module 290 and the comparison of the current signal to the target value may be implemented in P2 as a periodically running clock interrupt service routine that generates the first two stage PWM signal at 8. As shown in fig. 9, Fault _ Thd is a constant value, P1 is the period value of the first stage PWM signal, and Status is the PWM pulse Status flag. The variable target _ value is a target on-time value of the first-stage PWM signal, and the variable current _ value is an on-time value of the first-stage PWM signal calculated at the present time. The variable PWMT2 is the current time in the first-stage PWM cycle, and the value of the variable C1 is the value of the injection capability in the second-stage PWM control, such as the amount of ammonia gas that the injector 230 can inject during the energization open time P2.

As shown in fig. 9, when the interrupt service routine is triggered, the value of C1 will be calculated first, and then the value of PWMT2 will be compared with the period value P1 of the first stage PWM signal. If the current cycle is over, i.e., PWMT2> -P1, the value of the second stage PWM duty cycle Dc2 is checked. When the Dc2 value is less than P2, the total error for the current PWM cycle will be calculated and saved in the variable previous _ error. Thereafter, the current _ value is initialized in step 292, then the variable target _ value is updated for a new cycle, and the error to be corrected for the current cycle is calculated by adding the current error to the error of the previous cycle. If the error to be corrected is equal to or greater than C1, then the Dc2 value is set to 100% and the Status flag is set to ON, otherwise, the value of Dc2 is set to error/P2 and the flag Status is reset to OFF. After which the procedure ends. Returning to the comparison between the PWMT2 value and the P1 value, if the current cycle ends with a duty cycle value not less than P2 (Dc2> ═ P2), this means that errors cannot be corrected in that PWM cycle. In this case, the error in the previous cycle will be calculated and the PWMT2 value will be set to P2. Thereafter, current _ value will be initialized and the Status flag will be set to ON. This error accumulates due to the failure to correct the error. If the accumulated error is above the threshold Fault _ Thd, the interrupt routine ends after a Fault is reported. Returning again to the comparison between the PWMT2 value and the P1 value, when the PWMT2 value is less than P1 (the interrupt routine is called again in the same first level PWM cycle), the PWMT2 value will increment P2 and check the Status flag Status. If the Status flag Status is OFF, the value Dc2 is set to 0 and the procedure ends, otherwise current _ value is calculated in step 291 and the error to be corrected is updated thereafter. Before the end of the procedure, error value error is compared to C1. If the error value error is equal to or greater than C1, then the Dc2 value is set to 100%, otherwise the routine ends after setting Dc2 to error/P2 and resetting the Status flag Status to OFF.

As shown in fig. 9, the target _ value may be calculated using the reductant Mass flow command Mass _ flow _ rate _ cmd by the following equation:

target _ value (i) Mass _ flow _ rate _ cmd S0(F1), where S0 is the period value of the first-stage PWM signal.

The formula used to calculate current _ value in step 291 may be:

current _ value (i) ═ K × sqrt (pr (i) -Pe)) + current _ value (i-1) (F2), where i is the number of interrupts since PWMT2 reset to P2:

i ═ PWMT2/P2 (F3); sqrt is a square root calculation, K is a constant, pr (i) is a pressure sensing value in the i-th interrupt cycle, and Pe is a pressure in the exhaust passage 432.

The constant K may be calculated from the discharge coefficient CD of the injector, the minimum area An of the injector nozzle, and the density ρ of the reducing agent using the following formula: k is C _ D A _ n √ 2 ρ (1), and the value of current _ value (1) is set to 0 in step 292. The value of C1 may be calculated using the following formula:

C1＝K*sqrt(Pr(i)-Pe))*P2(F4)

as shown in fig. 10, the functionality of the third stage PWM duty cycle generation module 289 may be implemented in a periodically running clock interrupt service routine. As shown in FIG. 10, after the service routine begins, the value in the timer PWMT3 is compared with the On-Time value On _ Time2 of the second stage PWM signal. If the value of PWMT3 is less than On _ Time2, the duty cycle value of the third stage PWM signal Dc3 is calculated using a function of the Time terms PWMT2-P2+ PWMT 3. The time term is the time in the first stage PWM signal from the moment the cycle is triggered to the current time. A look-up table with this time term input may be used in the calculation of Dc3 so that more voltage levels may be generated. If the PWMT3 value is not less than the On _ Time2 value, then the Dc3 value is reset to 0. Thereafter, the PWMT3 value is increased by P3, where P3 is the period value of the third level PWM signal, and the PWMT3 value is compared to the P2 value. If the PWMT3 value is less than the P2 value, the routine ends; otherwise, the On _ time2 value is updated with the product of the Dc2 value and the P2 value, and the PWMT3 value is reset to 0, and the procedure ends.

The hollow vessel of the invention is also fluidly connected to the injector by an electrically controlled valve and the rate of delivery of ammonia is controlled by controlling the opening time of the electrically controlled valve in a repetitive cycle; if only ammonia is produced in the vessel, the delivery rate of ammonia being the mass flow rate of gas flowing through the sparger, and when multiple substances are produced in the vessel, calculating a correction factor to determine the delivery rate of ammonia; in order to precisely control the ammonia delivery rate, the present invention uses three-stage PWM control in which a first-stage PWM signal is generated by periodically updating the duty ratio of a second-stage PWM signal generator, and the duty ratio value is calculated from the flow value in the current period calculated using the pressure sensing value; the time from the moment of the first PWM cycle start to the current moment and the period and duty ratio value of the second PWM signal are also used for determining the duty ratio of the third-stage PWM signal; with three-level PWM control, feedback control of flow can be achieved without the use of a dedicated flow sensor, while the turn-on voltage and hold voltage can be provided to control the electrically controlled valve.

As shown in fig. 2, under the condition of cold start, it takes a relatively long time to decompose the solid reducing agent 458 by heating to make the pressure in the ammonia generating chamber 457 reach the minimum start-up condition of the reducing agent, that is, the pressure in the ammonia generating chamber 457 exceeds the pressure in the exhaust passage 432, because heat conduction and pyrolysis are required. And the lower the heating power of the electric heater 407, the larger the volume of the ammonia generating chamber 457, the longer this time will be. In order to rapidly generate the reducing agent under the cold start condition, and thus improve the low-temperature nox conversion efficiency, a small-volume buffer chamber may be connected in series in the metering injection system 200, and the rapid pressurization characteristic of the buffer chamber is utilized to accelerate the cold start process.

Claims

1. An ammonia gas generation metering injection device, characterized in that: the device comprises a metering injection control unit, a hollow container with an ammonia generating chamber, a cover matched with the hollow container, a solid reducing agent positioned in the ammonia generating chamber, an electric heater positioned in the ammonia generating chamber, a liquid discharge pipeline positioned at the bottom of the hollow container and provided with a liquid discharge valve, gas discharge pipes which are positioned on the solid reducing agent and are used for discharging gas accumulated in the solid reducing agent and are uniformly provided with openings, an exhaust passage which is communicated with the ammonia generating chamber through a check valve, an electric control valve used for controlling the injection rate of ammonia and an exhaust pipeline and is used for discharging ammonia gas, and an electric heating wire positioned in the exhaust pipeline; the ammonia generating chamber is internally provided with a first pressure sensor for sensing the internal pressure, a first temperature sensor for sensing the internal gas temperature and a second temperature sensor for sensing the solid reducing agent temperature, and the metering injection control unit is respectively connected with the electric heater, the electric heating wire, the electric control valve, the first pressure sensor, the first temperature sensor and the second temperature sensor through signal wires; the driving signal of the electric heater is a voltage pulse signal having a high current signal and a low current signal.

2. The ammonia gas generation metering injection device of claim 1, wherein: the closed-loop temperature control module of the electric heater comprises a current detection module, a pulse controller, a pulse width modulation generator and a driver, wherein the current detection module detects the current of the electric heater and sends a detection signal to the pulse controller, the pulse controller generates a signal duty ratio according to the detection signal and the temperature duty ratio and sends the signal duty ratio to the pulse width modulation generator, the pulse width modulation generator generates a pulse width modulation signal with a fixed period according to the signal duty ratio and sends the pulse width modulation signal to the driver, the pulse width modulation signal is converted into a driving signal in the driver, and the driving signal is sent to the electric heater through the current detection module.

3. An ammonia gas generating metering injection apparatus as defined in claim 2 wherein: the pulse controller comprises a current measuring module, a temperature calculating module and a temperature pulse control module, wherein the current measuring module converts a detection signal into a digital value, the temperature calculating module calculates the resistance value of the electric heater according to the digital value, then calculates the temperature value of the heater according to the temperature resistance curve of the electric heater, and the temperature pulse control module obtains the signal duty ratio according to the temperature value and the temperature duty ratio of the heater.

4. An ammonia gas generating metering injection apparatus as defined in claim 3 wherein: the control method of the temperature pulse control module comprises the following steps:

(2) incrementing a counter TimerON, wherein the TimerON is TimerON + 1;

(5) starting a temperature PID controller, and ending the program;

(8) incrementing a counter timerfoff, which is timerfoff + 1;

5. An ammonia gas generating metering injection apparatus as defined in claim 2 wherein: the pressure control module is used for generating a temperature duty ratio signal, and the temperature duty ratio signal is generated by calculation according to an error value obtained by comparing a pressure sensing value obtained by the first pressure sensor with a target pressure value.

6. The ammonia gas generation metering injection device of claim 1, wherein: the metering injection control unit is connected with the control valve through a signal line.

7. An ammonia generating metering injection apparatus as defined in claim 6 wherein the control method of the control valve includes the steps of: the pressure sensing value of the first pressure sensor is compared with a low pressure threshold value Thd _ PLo and a high pressure threshold value Thd _ Phi respectively, the control valve is electrically opened when the obtained pressure sensing value is smaller than the low pressure threshold value Thd _ PLo, and the control valve is electrically closed when the pressure sensing value is larger than the high pressure threshold value Thd _ Phi.